Russia's lower house of parliament, the Duma, has unanimously backed a bill placing adoption restrictions on nations that allow same-sex marriage.

The proposal seeks to ban adoption of orphans by foreign gay couples and by single foreign nationals from countries where same-sex marriage is legal.

It will become law when approved by the upper house and President Vladimir Putin; that is considered a formality.

France recently became the 14th country to legalise same-sex marriage.

Earlier this month, British peers also voted in favour of government plans to allow gay marriages in England and Wales.

But President Putin recently warned Moscow would change its laws to ensure same-sex couples would not be able to adopt Russian orphans.

"We respect our partners but ask them to respect Russia's cultural traditions and ethical, legal and moral standards," he said.

'Distorted perception'

Tuesday's second reading of the bill was passed by 443 votes to nil.

The amendments to Russia's family code say those banned from adoption would include "persons in a marriage union between people of the same sex registered in a state where such a union is allowed, as well as citizens of such states that are not married".

"Adoption of this bill de-facto eliminates the chance for foreign persons of so-called non-traditional sexual orientation to adopt Russian children," said one of the bill's authors, Yelena Mizulina, in televised remarks.

The bill is expected to be confirmed in a third and final reading on 21 June, then passed by the upper house and signed into law by President Putin.

"A child should have a mother and a father, a child in a family has an idea of what the world is about," said Duma deputy speaker Sergei Zheleznyak.

"If a child ends up with a homosexual couple, it could cause severe damage and the child ends up with a distorted perception of reality."

Last week, the Duma passed a law imposing heavy fines for providing information about homosexuality to people under 18.

Russia decriminalised homosexuality in 1993 and officially removed it from a list of psychiatric disorders in 1999.

But anti-gay sentiment remains high and has led to violent street clashes in recent weeks.

A recent poll found that nearly half of Russians believe that the gay and lesbian community should not enjoy the same rights as other citizens.